AZIMUTHAL SHEAR-WAVE VELOCITY ANISOTROPY IN THE BASIN AND RANGE PROVINCE USING MOHO PS CONVERTED PHASES

An eight-station large aperture seismometer army was deployed in the Basin and Range province of west-central Nevada for the 1988-1989 Program for Array Seismic Studies of the Continental Lithosphere (PASSCAL) Passive-source seismic experiment. During the 10 months of data collection a total of 100 teleseismic events were recorded (DELTA > 30-degrees). Source-equalized P wave receiver functions show waveform variations in timing, amplitude, and polarity in the Moho Ps phase that is diagnostic of shear wave velocity anisotropy. Information regarding the crustal anisotropic component can be recovered through the Ps phase since it is generated at the Moho and is sensitive to shear wave splitting in the crust only. We utilize single-event, sucked , and array-beam-formed receiver functions to minimize the influence of structural variations and scattering on the observed converted phases. Analysis of shear wave splitting of the Ps conversion from the crust-mantle boundary indicates a fast azimuth of anisotropy oriented approximately NW-SE with observed time delays of 0.20 s. This strongly suggests coherent crustal anisotropy with a fast direction perpendicular to the strike of fault block mountain ranges. This fabric is most likely due to the preferred crystallographic orientation of seismically anisotropic minerals in the middle to lower crust rather than the distribution of Basin and Range upper crustal fracture systems.